1. Field of the Invention
This invention relates to antifriction assemblies and, in particular, to antifriction assemblies of shaft and bearing, or of screw and nut members of particular construction and design.
2. Brief Statement of the Prior Art
Various designs have been employed for antifriction threaded members such as an assembly of a screw and nut. Typical of these are the members having peripheral roller elements in the nut member such as that described in U.S. Pat. No. 3,406,584 or 3,648,535. The construction of these members is relatively complex, requiring a nut member housing which rotatably supports a plurality of peripherally disposed roller members having helical external threads to function as planet elements about the central, threaded screw shaft. The complexity of design of these assemblies results in a high initial cost and maintenance requirement. Accordingly, this design is not ideally suited for use in remote installations or in equipment where high initial cost is to be avoided. Typical of such installations is the damper actuator for controlling the position of dampers of conventional heating and cooling installations. Commonly these are actuated by a motor that drives a rotatable member such as a threaded shaft on which is carried a traveling nut member which is mechanically connected to the damper, thus serving as a transducer of rotary to reciprocal motion.
Attempts to substitute the metallic elements of conventional threaded assemblies with plastics have generally been unsuccessful. The direct substitution of plastics for metals in the construction of screw and nut members results in assemblies which exhibit excessive wear and frequent failure. Attempts to obviate this behavior and extend the life of the plastics elements have generally been pursued along the design parameters of metallic threaded members, typically directed toward reducing the specific loading on the members by increasing the bearing surface areas. This practice has been followed despite the knowledge that some plastics such as the fluorocarbons, polyamides and acetal resins, among others, have coefficients of friction which are inversely proportional to compressive loading on bearing surfaces of such plastics.